Although IQ is often believed to stay relatively stable during a person's life, new research suggests there can be significant swings - both up and down - during teenage years, resulting from changes in the brain.
Credit: Veer
Researchers identified regions of the brain where levels of grey matter changed. This image shows the functional activations in the regions identified by the structural analysis.
Credit: Ramsden et al. Nature
LONDON: Rather than being fixed over our lifespan, a person's IQ can show both significant increases and decreases during their teenage years, new results suggest.
Reported in Nature today, the results reveal that verbal and non-verbal ability, as measured by IQ (Intelligence Quotient) tests, fluctuated over a period of three to four years during adolescence. They also showed that these changes correspond to specific structural changes in brain regions associated with speech and movement.
These findings, while implying that early achievers might not achieve their potential, and that upward swings in IQ are possible, also has implications for the testing and screening of children in their school years.
"IQ has traditionally been regarded as essentially fixed over the lifespan - apart from the effects of neurological insult or degenerative conditions," said Cathy Price, co-author of the study and a professor in the Wellcome Department of Cognitive Neurology at University College London.
"However, our results show that abilities are changing in the teenage years, and that the direction of change may be different for verbal and non-verbal skills. We confirmed that these changes were not just random variation in performance on tests … by noting that they correlated with changes in the structure of particular areas of the brain."
Identifying intelligence
IQ has generally been thought to be relatively stable across lifespans. Save for dramatic experiences, such as dropping out of school, that effectively stunt learning, it is expected that a 'normal' lifespan will involve a more or less predictable IQ development.
Though evidence to the contrary is pervasive, many have dismissed such changes as "measurement error", meaning that the IQ test is not perfectly reliable and, hence, prone to fluctuation. According to that theory, general intelligence is still stable - the problem is the test.
The new study, by showing that IQ changes correspond to specific brain changes, questions this logic, suggesting that adolescent IQ fluctuation is not a problem of measurement, but a physical reality.
Brain matters
Identifying different brain areas for different IQ measures has been difficult to achieve in previous studies looking at single-test performance. By incorporating a longitudinal and comparative dimension, the researchers were able to shed light on important elements of intelligence and its physical manifestation.
Price and colleagues studied 33 adolescents throughout their teenage years. They conducted one initial IQ test and corresponding brain scan when the participants were between 12 and 16 years of age, and once again when the participants were between 15 and 20 years of age.
The researchers measured each subject's verbal IQ (language, arithmetic, knowledge and memory) and their non-verbal IQ (visual puzzles), looking to see if they could find interesting correlations between performance and physical brain development.
The researchers were able to identify two areas of the brain for verbal and non-verbal IQ, respectively. Increases of grey matter in the left motor cortex - the so-called 'speech region' of the brain - successfully correlated with verbal IQ, while increase in non-verbal IQ correlated with denser grey matter in the anterior cerebellum - the area associated with hand movement. These, however, are not symbiotic - they can increase or decrease independently of one another.
